<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    html,body{
      margin: 0;
      padding: 0;
      width: 100%;
      height: 100%;
      background-image: linear-gradient(to bottom right,red,gold);
      display: flex;
    }
    .box{
      width: 400px;
      height: 250px;
      background-color: rgba(255, 255, 255, .6);
      margin: auto;
      display: flex;
      font-size: 80px;
      justify-content: center;
      align-items: center;
    }
    .box div{
      margin: 0 5px;
    }
  </style>
</head>
<body>
  <div class="box">
    <div id="HH">00</div>
    <div>:</div>
    <div id="mm">00</div>
    <div>:</div>
    <div id="ss">00</div>
  </div>
  <script>
    let HH=document.getElementById('HH')
    HH.innerHTML='09'
    let mm=document.getElementById('mm')
    mm.innerHTML='06'
    let ss=document.getElementById('ss')
    ss.innerHTML='18'
  </script>
</body>
</html>